Polyoxyalkylene polyols suitable for the preparation of polyurethanes can be obtained via various preparation processes. One process of significance on the industrial scale is the base-catalyzed addition of alkylene oxides onto H-functional starter compounds, and another is the use of double metal cyanide compounds as catalysts (“DMC catalysts”) for the addition of alkylene oxides onto H-functional starter compounds. The (Lewis) acid-catalyzed addition of alkylene oxides onto suitable starter compounds is of minor importance.
Under alkali metal hydroxide catalysis, there is a distinct increase in unwanted side reactions with rising molar mass of the polymer. Particular mention should be made here of the isomerization of propylene oxide to allyl alcohol, which, at high equivalent molar masses (or low OH numbers), leads to a high proportion of monofunctional polyoxyalkylene species in the reaction mixture and hence to significant lowering of the functionality. The monofunctional polyoxyalkylene molecules therefore have an adverse effect on the through-curing characteristics and the profile of physical properties of polyurethane systems or other materials producible from these polyoxyalkylene compounds, for example silane-based sealants that are curable under the action of air humidity.
The use of DMC catalysts has made it possible to advance the addition of alkylene oxides, especially propylene oxide, onto H-functional starter compounds down to very low OH numbers, i.e. high equivalent molar masses, without any significant degree of occurrence of the abovementioned isomerization of propylene oxide to allyl alcohol. Highly active DMC catalysts which are described, for example, in U.S. Pat. No. 5,470,813, EP-A 700949, EP-A 743093, EP-A 761708, WO-A 97/40086, WO-A 98/16310 and WO-A 00/47649 additionally have exceptionally high activity and enable polyoxyalkylene polyol preparation at very low catalyst concentrations (100 ppm or less), such that removal of the catalyst from the finished product is no longer required. A typical example is that of the highly active DMC catalysts which are described in EP-A 700949 and contain not only a double metal cyanide compound (e.g. zinc hexacyanocobaltate(III)) and an organic complex ligand (e.g. tert-butanol) but also a polyoxyalkylene compound having a number-average molecular weight greater than 500 g/mol.
The equivalent molar mass of materials containing active hydrogen atoms is understood to mean the total mass of the material containing active hydrogen atoms divided by the number of active hydrogen atoms. In the case of materials containing hydroxyl groups (for example polyoxyalkylene polyols), they are related to the OH number (hydroxyl number) as follows:equivalent molar mass=56100/(OH number [mg KOH/g])  (I)
The equivalent molar mass of the polyoxyalkylene polyols is thus ascertained according to formula (I), where the hydroxyl number of the polyoxyalkylene polyol is determined according to DIN 53240. The calculated equivalent molar mass is determined by inserting the calculated OH number into formula (I). The calculated OH number (OH numbercalc) is determined by formula (II):OH numbercalc=((mass of the starter used)×(OH number of the starter))/(total mass of polymerization batch)  (II)
In the present patent specification, reference is made to the calculated equivalent molar mass since even DMC catalysts cannot convert alkylene oxides to polyoxyalkylenes completely without side reactions. This is naturally manifested particularly in the high target equivalent molar masses under consideration in the present patent specification.
The DMC-catalyzed preparation of alkylene oxide addition products having high equivalent molar masses and the use thereof for preparation of polyurethane- or polyurea-based materials are known to those skilled in the art. For example, DE-A 4117679 and U.S. Pat. No. 5,096,993 disclose the use of polyhydroxy or polyamine compounds having molar masses of up to 30 000 Da for preparation of soft polyurethane or polyurea elastomers by the reactive injection molding process (“RIM” methodology). WO-A 9104997 discloses polyoxyalkylenetriols having molar masses of up to 30000 Da as polyoxyalkylene component of isocyanate-terminated prepolymers which are used in high-quality polyurethane sealant systems. EP-A 1316573 discloses a process for obtaining rapidly demoldable flexible foam bodies having good sustained use properties, the production of which involves using polyoxyalkylene polyols having equivalent molar masses of preferably 5000 to 11 000 Da that have been prepared by DMC catalysis as polyol component. EP-A 0425694 discloses isocyanate-terminated polyoxyalkylene prepolymers, the polyoxyalkylene component of which has equivalent molar masses of up to 15 000 Da. Polyoxyalkylene polyols of this kind are obtained via DMC catalysis. Polyoxyalkylenes prepared via DMC catalysis and having equivalent molar masses of up to 15 000 Da are used in EP-A 0723561 as starting compounds for production of moisture-curing sealant systems based on polymers containing silane groups.
In the DMC-catalyzed preparation of polyoxyalkylene polyols having very high calculated equivalent molar masses (9500 Da or higher), the achievement of processible viscosities becomes problematic with increasing calculated equivalent weight. WO-A 2013/000915 proposes solving this problem by metering the alkylene oxides into the reactor within 15 to 23 h. If the alkylene oxides are supplied to the reactor within this metering time window, it is indeed possible to obtain polyoxyalkylene polyols of relatively low viscosity with high calculated equivalent molar masses. However, a distinct disadvantage of this process is the long run time of the individual polymerization batches which limits the plant capacity (space-time yield).